Expert: The Most Efficient Way To Use Energy-Efficient CFL, LED Bulbs

Handout, Handout

Getting out the most out of your energy-efficient bulbs.

Getting out the most out of your energy-efficient bulbs. (Handout, Handout)

How to extend the life of CFL bulbs.

Live longer by quitting smoking, drinking moderately, exercising regularly, limiting stress and eating a bowl of porridge every day. Great advice for a human, but terrible for a compact fluorescent light bulb or LED.

So how, asks George Coshow of Middle Haddam, to treat your bulbs? Terry McGowan, the American Lighting Association's director of engineering, answers his specific questions:

Q: How are CFLs affected by turning them on for less than 15 minutes? I've been told there is a warm-up time. Does lesser time lead to reduce longevity, or is it just that CFLs don't achieve their potential efficiency until warmed up?

A: CFL bulbs are a type of fluorescent lamp. Such lamps depend upon ionized gas inside the tube to transform electricity into visible light.

The gas involved is mercury vapor. Because mercury is a liquid at room temperatures, there can be a delay of a few minutes, when a CFL is first turned on, to reach full light output as the mercury turns from a liquid into a gas inside the tube. That's a normal process for every fluorescent lamp and it has no significant effect on lamp life.

CFL life depends mainly upon two factors: burning time and number of starts. At the ends of the fluorescent tube in a CFL are electrical terminals called electrodes. These electrodes are coated with an emission material that gradually sputters off as the bulb operates.

When the emission material is all burned off of one of the electrodes, the bulb won't start or will flicker and that means the bulb is at the end-of-life. Starting burns off more of the electrode coating than does bulb operation so starting the bulb is the same as operating it for several hours from a lamp life standpoint.

When CFL bulb manufacturers rate bulb life, they assume a number of hours of operation per start. That results in typical life ratings of 8,000 to 10,000 hours. CFL bulbs started frequently — say a bulb used in a bathroom that is turned on and off many times per day — will therefore have a shorter life than rated. Energy Star (1.usa.gov/1DFsP5t) recommends a 15-minute operating period per start for CFLs to minimize effects on lamp life.

CFLs may fail for reasons other than wear-out because they are electronic devices with integral ballast circuitry — that's what's inside the plastic capsule between the base of the bulb and the spiral glass fluorescent tube — and there are dozens of parts that could potentially fail due to voltage surges, poor quality or high-temperature operation.

Q: In a situation where I may be in and out several times during the day — such as my basement work area — is it more efficient to leave a CFL on all day rather than on-off for 30-minute periods?

A: The 15-minute period of operation per start recommended by Energy Star is a good compromise between energy use and lamp life. Leaving the lamp burning to conserve lamp life is, in several ways, a false saving because energy use includes not only the direct costs of the energy itself, but also environmental costs of burning fuel.

Note that as CFL bulb prices go down, the economical burning period per start is less as well because energy costs become a higher proportion of total operating costs of buying the bulb and operating it. I definitely do not recommend leaving a CFL on all day to preserve lamp life.

Q: How is bulb life affected in a three-way CFL as I commonly cycle through the settings on my way to max light for reading?

A: If you install and use a CFL three-way bulb, the normal switch action (low, medium and high) most likely triggers the ballast circuitry to send different levels of current through the fluorescent tube while it remains on. The result is little to no effect on lamp life. I say "most likely" as there have been some double-tube three-way lamps made where the tubes themselves are switched on and off to get the different levels of light; but they are uncommon and relatively expensive.

Q: Are LEDs best used in any manner different from on and off?

A: LED bulbs are not sensitive to on-off cycling so there is no effect on life. LED bulbs can be dimmed, but the bulb must be marked dimmable and matched with the appropriate type of dimmer for best results.

LED dimming technology is still evolving and the result is that current LED bulb products dim more smoothly and over a greater range than previous models. There are also some bulbs on the market now with a "warm dim" feature that changes the color of the light from the bulb to a warmer tone as the bulb is dimmed — much like an incandescent bulb.

LED products, especially lighting fixtures such as task lights, floor and table lamps are moving toward having two control features. One is dimming; the other is color control. The latter is used so that the "tone" of the light (chromaticity) can be adjusted through a range from "warm" to "cool" as desired.